In episode 244, today's guest gave us a vital wrinkle in how we interpret arterial lines during cardiac arrest. In this episode, we do the same thing to ETCO2. This a deep dive into the intricacies and pitfalls of using this monitoring modality during arrest.
Today's Guest
Per-Olav Berve is a Norwegian anaesthesiologist who works for the Oslo air ambulance and in-hospital at the Oslo University Hospital. He is currently wrapping up a PhD on CPR physiology, focusing on multimodal monitoring. His main project is a OHCA study on mechanical active compression-decompression CPR. (Bio from scanFOAM).
Pre-Tidal CO2 during Cardiac Arrest and the Interpretation of Waveforms
A majority of the conversation revolves around this paper:
- Lesimple et al. A novel capnogram analysis to guide ventilation during cardiopulmonary resuscitation: clinical and experimental observations
This is the critical image that I addressed in the podcast:
this image further clarifies the point:
So 3 patterns of cardiac arrest waveforms;
Regular
Indicative of good degree of thoracic filling. Looks like Bart Simpson's head throughout the entire wave
Intrathoracic Airway Closure
Minimal or no oscillations from chest compressions and rising throughout waveform
Indicates underfilled lungs/low FRC
Consider PEEP
Thoracic Distension
Absent or minimal oscillations at the beginning of the waveform until expiration of adequate volume to allow oscillations
Indicative of overfilled lungs
Consider reducing minute ventilation
The Numeric Value Lies
You need to look at the waveform, not the algorithm generated
TTE for Chest Compression Efficacy
TTE POCUS subcostal view is doable during compressions. Skulec et al. found good enough pics for scientific use in> 50% of patients. Of note: RV compressions contribute to EtCO2, but less likely to improve blood pressures than LV compressions
PO aims the subcostal probe so the lv is centered on the screen, then he can look at the angle and distance in cm and find the projected optimal spot for compressions
CO2 Min or Max
Still a ? of which of these two values is most relevant
Additional New Information
Here is the Paper from AHA that was mentioned:
Circulation 2013 Jul 23;128(4):417-35. [doi: 10.1161/CIR.0b013e31829d8654] Cardiopulmonary resuscitation quality: [corrected] improving cardiac resuscitation outcomes both inside and outside the hospital: a consensus statement from the American Heart Association
Lower Inflection Point (Closure of Alveoli) Decreases as CPR Goes On
More on EMCrit
Additional Resources
Professor
Nassau University Medical Center
No conflicts of interest (coi).
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thanks Scott and PO Berve.
completely new info for me here… still not sure how I might incorporate the wave form patterns in my next codes, but it is clear that the situation is more than simply the end tidal CO2 number … how to be expert in the waveforms is the new homework.
Scott , we need to talk about TEE at the next RLA hangout. as you might know, Hannepin has about about TEE scopes, and I think they employ them on most codes. I’ve heard your conversations with Filipe Teran.
thanks again to you both
tom fiero
correction: “…Hannepin has about five TEE scopes”
Hi Thomas! Thanks for you comments! First, I agree that the work of Filipe Teran and others pioneering TEE during chest compressions is immensely important. The benefits of TEE compared to our TTE approach are obvious. TEE is more precise and has better trending possibilities. I think it has a great potential for research. However, in trained hands will our TTE approach be faster, and more portable. I do not think these strategies should be considered as excluding to each other, rather as TTE first for coarse assessment, then TEE for precision ASAP. Second: regarding your planned capnography homework –… Read more »
Hi Scott and Per-Olav. Great episode, thanks for the deep dive on this. Scott, you mentioned a paper that you called “ACLS for actual resuscitationists”. Could you post the actual title or a link to this paper? Sounds like a great read.
not finding it immediately. Published by AHA. Can be found on AHA’s website. If you find it, let me know so I can add the citation here.
Great episode, thanks to you both. Is it this one?
https://pubmed.ncbi.nlm.nih.gov/23801105/
that’s it!!!!!
Very nice episode, thanks Scott and Per Olav!
Is the end decompression the thing to look for as the best compression site? I would think that the point which gives the highest systolic pressure would be the sweet spot for compression of the LV. In my mind end decompression pressure is for dosing adrenaline?
Normal lv pressures varies between systolic pressure and almost zero, but the diastolic pressure is a product of aortic recoil and vascular tone.
Hi Erlend! Great question! I think you refer to a brilliant observation: The SBP responds obviously and rapidly to chest compression related events and the End Decompression phase Pressure (EDP) sometimes seem to lag a little behind. You are most likely right in that the SBP is more useful in this regard than what the decompression pressure paradigm dictates. An increase of the SBP is a positive and wanted effect of a change in the compression point, and I would consider it beneficial, even if the capnometric peak reading does not change much. In addition, the beauty of the EDP… Read more »
Excellent discussion on an interesting topic! There’s one thing I’d like to clarify: PO made an important point the capnography monitors flow & not pressure per se, and gave an example scenario that capnography reading may drop “paradoxically” when the site of compression is moved from RV to LV, despite if an arterial line is in place you may observe better ABP because of improved LV SV. I wonder if this response is only quite transient that the CO2 reading should go back up quickly, because RV SV & LV SV should roughly match with each other in an equilibrium… Read more »
Hi Jonathan! Thanks for commenting on this. And of course you are right. During “stable” CPR with at stable ventilation pattern, changes in the peak capnometric reading (sorry for stressing that terminology) will be caused by changes in cardiac output. Thus, if CO is stable the peak capnometric reading is stable. Most often, all values will improve when you compress the LV better (except that darn “diastolic” reading on the monitor, but the EDP will improve, see my response to Erlend above). My point is that when I have a second monitoring modality, like an IBP line or cerebral oximetry, I… Read more »
Hi PO and thanks for clearing up the concepts! Many of this stuff is quite new to me and I really enjoy learning from you! It’s very true that the equilibration of arterial & venous pressure can occur surprisingly quickly. In my mental model, this happens in the form of volume redistribution when the blood in the arterial system (higher pressure & lower compliance pre-arrest) “discharging” into the lower pressure & higher compliance/capacitance venous system, ultimately overloading the RV. And I personally find RV volume overload (in the absence of increased RV afterload such as in the case of PE)… Read more »
Thanks for all the comments amigos! I will try to respond to each one of you. You are obviously highly skilled and smarter than me – I have spent a lot of time with a very good dataset to grasp concepts that you seem to understand intuitively. I consider physiology to be a constant struggle for a shared mental model. We will never be able to fully capture the full complexity of CPR. The quest then becomes how to decipher and distil our approximated models into something useful for the patient. Please consider most of my answers in this context, and… Read more »
Why not use a device like the EOlife, that is specifically designed to guide the manual ventilation and so simple to use that a 5 year old would be able to use it… https://youtu.be/nY5LRSlNweI Aș per the recent paper from Counts et Al, “Novel devices that measure changes in volume and pressure throughout the ventilation cycle will likely allow more accurate understanding of all ventilation parameters.12 Waveform capnography has been used extensively, though is influenced by a number of physiological parameters including minute ventilation, alveolar and anatomic dead space, cardiac output (native or augmented by chest compressions), and chest compression- related… Read more »
Hi Claude! Thanks, I was not aware of this product. Cool device, and I will check it out. I do believe we will se more of these type of flow metric solutions (most of these have limited capability to display ventilation pressure data). However, Laerdal also have its version of this with integrated capnometry, as used by Monica Thallinger in her neonatal resuscitation. That said, I would need to be very certain about the performance of these devices before I use them in the research setting. We have looked into using transthoracic impedance as a non invasive tidal volume estimate… Read more »